There is an ever increasing interest in the deployment of autonomous devices for monitoring biological, chemical and physical conditions in aquatic environments. This interest encompasses monitoring hydrographic conditions, fisheries, weather prediction, and global change in the open ocean. It also includes estuaries where interest arises from concerns about pollution, harmful algal blooms, living resources and biological diversity.
Reflecting the need for autonomously collected data, the advances in technology have produced reasonably affordable instrumentation capable of collecting and telemetering data. However, biofouling remains a major problem that to date has not been adequately addressed. The amount of growth that can accumulate in and around sensors over periods as short as 5 days can be great in high nutrient estuarine environments. Biofouling is, for a large percentage of instrumentation deployments, the single biggest factor affecting the operation, maintenance, and data quality of in-water monitoring sensors, and therefore biofouling prevention for sensor systems is considered a major issue in aquatic environment monitoring.
The scientific community recognizes that not only should sensors of monitoring devices be protected from biofouling, but additionally the environment surrounding the sensors must also be protected since in some cases, fouling can become so extreme that one can question whether the sensors are sampling the ambient water or a microenvironment controlled by the activities of the fouling organisms.
The biofouling of ships and instrumentation is typically controlled through the use of toxic paints incorporating metal biocides, e.g. cuprous oxide, and organometals, e.g. tributyltin. Anti biofouling paints cannot be put directly on the sensors and may not be sufficiently soluble to provide a “halo” effect that will protect the sensors. In addition, anti-biofouling paints can sometimes accumulate films that could inhibit sensor performance, after short periods of immersion. Also, mechanical systems, such as anti-fouling wipers have been developed and used in multi-parameter monitor devices. However, the anti-fouling paints are extremely toxic and thus are harmful for living organisms, while wipers do not have the capability of complete prevention and removal of bio-fouling, thereby only partially addressing the bio-fouling problem. These wipers can also become substrate for fouling organisms and thus scratch optically clear surfaces.
Usually, deployed instrumentation is serviced weekly or biweekly (depending on a region and season) to remove deposits of bio-organisms from the sensors or to replace the deployed sensors with cleaned and recently calibrated sensors. This is a time and cost consuming endeavor which makes aquatic environments monitoring extremely expensive and labor intensive.
There is therefore a need and ever increasing interest in monitoring of chemical and physical conditions in aquatic environments to provide autonomous devices capable of extended instrument deployment and of obtaining uncorrupted data by controlling the biofouling and eliminating the effect of biofouling on device operations.